Non-inflammable hydraulic fluid



.are operated largely by hydraulic means.

United States Patent NQN-INFLAMMABLE HYDRAULIC FLUID Jones]. Wasson, Union, and Arnold J. Morway, Clark Township, Union County, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application January 2, 1952,

. Serial No. 264,685

4 Claims. (Cl. 252-76) The present invention relates to an improved noninflammable hydraulic fluid of the glycol-water base type. It relates further to a hydraulic fluid of the type mentioned above having an improved viscosity index and a superior lubricating or wear preventing quality. Also, it has improved resistance to rust of ferrous metals in addition to its property of non-inflammability.

In the prior art numerous hydraulic fluids have been proposed. Some of these are of the hydrocarbon type which are advantageous for many applications but which arerather highly inflammable and unsuitable for certain uses. In industrial operations, such as the die casting of metals, for example, the controls of the casting machinery The hydraulic fluids used in such controls have frequently been a source of fire and danger. For this reason there is a growing demand for non-inflammable hydraulic fluids. Fluids of glycol-water blends have been investigated for vthis purpose. They are not absolutely non-inflammable but their resistance to flame is so much greater than that of the hydrocarbon oils that they may be considered substantially non-inflammable.

On the other hand, although the flame resistant propertiesof the glycol-water base fluids have long been recognized, these fluids have left much to be desired in several important respects. They are usually too thin or. non-viscous for hydraulic use and consequently must be thickened by addition of a more viscous material. The choice'of thickeners compatible with glycol-water blends has been limited and it has been rather difiicult to find thickeners which are entirely suitable for use with such blends. Unless the thickener is compatible, the solution of course is unstable, the thickener tending to settle or sludge out and to interfere with proper operation of the fluid or the mechanism in which it is used.

Furthermore, as suggested above, the Water-glycol base hydraulic fluids have relatively very poor lubricating characteristics. While hydraulic fluids are used primarily to transmit forces through hydraulic means, they must also provide lubrication for hydraulic pumps and associated mechanical parts in order to prevent excessivewear. The prior art hydraulic fluids of this type have been poor lubricants, on the whole. Many of them have permitted rusting of ferrous metals which, of course, is highly objectionable. Aside from the damage done by the rust itself the parts frequently stick, or freeze, so that the operation of the mechanism becomes uncertain and erratic. In vital hydraulic controls, particularly, such erratic operation cannot be tolerated at all and it is always unsatisfactory.

It has long been known that certain of the long chain fatty acids, e. g. oleic acid, and glycerides thereof, have some useful friction or wear reducing properties in mineral base oils. The soaps of such materials have been used in lubricating oils also. They are not compatible with glycol-water base fluids, however, and users have been compelled to resort to other materials.

2,737,497 Patented Mar. 6, 1956 The present invention is based-on the discovery that a glycol-water base hydraulic fluid, provided with a suitable thickener to raise its viscosity to a suitablelevel, may be materially improved 'inits lubricating. and rust preventive properties by adding thereto :the soap orisoaps of one or more polybas'ic aliphatic acids. Thesoap selectedmust of course be soluble .in the glycol-waterblend. The soaps of .such saturated :acids sebacic, adipic, azelaic, and ingeneral the homologous'acids having from .6' to' about 18 carbon atoms, or more in some cases, are quite useful for this purpose. Aspointed .out in a co"- pending application .filed contemporaneously herewith, Serial No. 263,972 certain branched chain aliphatic'a'cids also produce soaps which have good water-soluble properties but the present'inventi'onrelates to the polybasic 'acidsoaps, and: especially the scam of the dicarboxylic aliphatic acids. 1

Certain polybasic acid soaps of relatively high molecular weight have also been discovered to have the required properties of'wat'er solubility to at least a limited degree. These are also contemplated for "use in the present invention. Thus, a so=called dimer acid; sold alongwith small amountsof higherjpolymers, has been found to be quite satisfactory for making the soaps; I-ligh molecular weight acids marketed by Rohm and Haas under the trade: name VR- l having amolec'ular'weight approaching 1000' and anfaver'age' of nearly 2 carboxyl groups per molecule are'alsovery satisfactory.

In general, abou't 0.5 to2% by weight of the alkali metal soaps of the polybasic acids are preferred. The polybasic acids themselves should be fairly well saturated for stability, although a moderate amount of unsaturation may be tolera'ted as in the dimer acid mentioned above; While this particular acid appears to be essentially a dimer of linoleic acid, it will be understood that trimers, tetramers, etc. can be used, as well as other di-, tri-, tetra-, etc, carboxylic acids, so long as their alkali metal soaps are adequately soluble in the base fluid.

As described in the copending application mentioned above, the preferred thickener is a polymeric alkylene glycol or glycol-ether material such as'that sold'by Carbide and Carbon Chemicals Corporation, under the trade name of Ucon H ',000 Polymer. This thickener itself has a viscosity of about 90,000 S. S: U. at F. d

The related polymer glycols' and polyglycol ethers of viscosity range from-about400 up to about 200,000 S. S.- U. at 100 F. may be used. Others which are available are sold by Carbide and Carbon Chemicals Corporation under the trade names Ucon 75H-490, Ucon 75H-1400 and Ucon 75H-9150. The last figure in each of these products apparently is a rough indicator of viscosity at 100 F. Also, the polyglycols of similar viscosity may be used so long as they are fully compatible with and a flash point of 485 F., and a specific gravity at 20/20 C. of 1.095.

rather widely. In general, the composition may preferably consist of about 40 to 65% by weight of water, about 9 to 34% of a glycol, preferably ethylene glycol and about 20 to 30% of the polymeric thickener. A

wider range of to 40% thickener may be used where viscosity requirements permit. The thickener, in any case, should be present in such quantity and of sufiiciently high molecular weight to increase the viscosity substantially above that of the glycol-water base.

The preferred soaps of the polybasic acids are those of sodium, but the soaps of the other alkali metals, potassium and lithium, can also be used. It will be understood that these soaps are used primarily to improve lubrication or prevent wear and also to inhibit metal rust and corrosion. In general, the soaps of the po1yvalent metals arenot as satisfactory. Suitable auxiliary rust inhibitors and modifying agents may, of course, be incorporated as is well known to those skilled in the art. The invention will be more fully understood by reference to the following specific examples.

EXAMPLE I Weight percent composition Water 62.8 Ethylene glycol 11.2 Ucon 75H-90,000 polymer 25.0

Sodium soap of Emery M461R acid 1 1.0

A commercially available dibasic acid mixture primarily composed of dilinoleic acid and having a molecular weight of about 600, an iodine value of 80- 95, an acid value of 180-192, and a saponification value of 185-195.

The composition of Example I was tested in the stand ard four ball wear test wherein three ball bearings onehalf inch in diameter are clamped together and a fourth ball of the same size is rotated on top and in contact with the three under an applied load. Standard test conditions call for. operation at a temperature of 167 F., with an applied load of 10 kg. for one hour. The scars produced on the three stationary ball bearings are measured and their average is taken as the wear scar diameter in millimeters. Test results are shown below on the formulation of Example I and on additional compounds tested including those prepared from the high molecular weight dibasic acid sold by Rohm and Haas under the trade name VR-l and the sodium soap of sebacic acid.

4-ball wear tester results A commercially available dibasic acid having a molecular weight of about 1,000, an acid number of 150, an iodinenumber of 36, and a. saponificatlon number of 172.

The composition of Example I was also tested for rust inhibition. A specimen of clean sheet steel immersed in this composition for 30 days remained free of rust for 30 days. The same fluid, without the soap, showed heavy rust in less than 24 hours.

It will be noted that the glycol-water base product including thickener but not a soap showed a veryhigh wear as indicated by the 1.5 mm. scar diameter. The other products containing one of the desirable'soaps exhibited excellent anti-Wear properties, being in the same general range as typical mineral oil lubricants. Since water-base hydraulic fluids ordinarily give considerably higher wear than mineral oil lubricants, it will be noted that the improvement obtained with the above fluids is very substantial.

It appears that the molecular weight of the soap should be as high as is consistent with good solubility in the base.

A compromise must often be made and the amount of soap which can be dissolved is often limited in the case of the higher acid products. In general, the soaps should be prepared from acids of at least 8 carbon atoms and they may run up to products having molecular weights as high as 1000 or more, provided the structure of the acid is such that the soap remains water soluble.

What is claimed is:

1. A substantially non-inflammable hydraulic fluid comprising from 40 wt. per cent to wt. percent of water, and from 9 wt. percent to 34 wt. percent of ethylene glycol as a water-glycol base, from about 5 wt. percent to 40 wt. per cent of a polymeric thickener selected from the group consisting of polyalkylene glycols having viscosities of from about 400 to about 200,000 S. U. 'S. at F., and about 0.5 wt. percent to 2.0 wt. per cent of an alkali metal soap of a polybasic aliphatic acid which is soluble in said water-glycol base, said acid being substantially a dimer of an unsaturated fatty acid having from 12-22 carbon atoms per molecule.

2. A'hydraulic fluid composition consisting essentially of about 40 to about 65 wt. per cent of water, about 9 to about 34 wt. per cent of ethylene glycol, about 20 to 30 wt. per cent of a polyalkylene glycol of a viscosity of about 90,000 S. U. S. at 100 F., and about 0.5 to about 2.0 wt. per cent of an alkali soap of a mixture of dibasic acids consisting essentially of a dimer of linoleic acid.

3. Composition according to claim 1 wherein the soap is a sodium soap of essentially dimeric linoleic acid soluble in the water glycol base.

4. Composition according to claim 2 wherein the alkali metal is sodium.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,148 Berliner June 20, 1933 1,928,956 Tatter Oct. 3, 1933 2,324,770 Donlan July 20, 1943 2,426,496 Farley Aug. 26, 1947 2,558,030 Zisman et a1 June 26, 1951 

1. A SUBSTANTIALLY NON-INFLAMMABLE HYDRAULIC FLUID COMPRISING FROM 40 WT. PER CENT TO 65 WT. PERCET OF WATER, AND FROM 9 WT. PERCENT TO 34 WT. PERCENT OF ETHYLENE GLYCOL AS A WATER-GLYCOL BASE, FROM ABOUT 5 WT. PER CENT TO 40 WT. PER CENT OF A POLYMERIC THICKENER SELECTED FROM THE GROUP CONSISTING OF POLYALKYLENE GLYCOLS HAVING VISCOSITIES OF FROM ABOUT 400 TO ABOT 200,000 S. U. S. AT 100*F., AND ABOUT 0.5 WT. PERCENT TO 2.0 WT. PER CENT OF AN ALKALI METAL SOAP OF A POLYBASIC ALIPHATIC ACID WHICH IS SOLUBLE IN SAID WATER-GLYCOL BASE, SAID ACID BEING SUBSTANTIALLY A DIMER OF AN UNSATURATED FATTY ACID HAVING FROM 12-22 CARBON ATOMS PER MOLECULE. 